1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly to a two-domain in-plane switching (IPS) mode thin film transistor (TFT) LCD device.
2. Description of Prior Art
In a conventional liquid crystal display, a pair of facing transparent electrodes is respectively formed on two substrates, and is used for driving a liquid crystal layer therebetween. In such a device, a displaying means known as a TN (twisted nematic) display is adopted. That is, the liquid crystal display operates by being supplied with an electric field having a direction orthogonal to inner surfaces of the substrates.
However, the TN mode LCD has a narrow viewing angle, which means that the quality of the display greatly depends on the direction of viewing. In order to obtain a wide viewing angle, the IPS type LCD has been developed.
A detailed explanation about operation modes of a typical IPS-LCD device is provided hereinbelow, with reference to FIGS. 5 through 7.
As shown in FIGS. 5-6, the IPS-LCD device 1 comprises upper and lower substrates 11 and 12 spaced apart from each other, and a liquid crystal layer 17 sandwiched therebetween. The substrates 11 and 12 are called a color filter substrate and a TFT substrate, respectively. A multiplicity of pixel electrodes 16 and a multiplicity of common electrodes 15 are disposed on the lower substrate 12. The pixel electrodes 16 and the common electrodes 15 are parallel to but spaced apart from each other.
When no electric field is applied between the pixel and common electrodes 16 and 15, long axes of liquid crystal molecules in the liquid crystal layer 17 maintain a predetermined angle relative to the pixel and common electrodes 16 and 15.
As shown in FIG. 7, when a voltage is applied between the pixel and common electrodes 16 and 15, a horizontal in-plane electric field that is parallel to a surface of the lower substrate 12 is established between the pixel and common electrodes 16 and 15. The liquid crystal molecules are twisted so as to align according to the electric field. That is, the long axes of the liquid crystal molecules are oriented perpendicular to the pixel and common electrodes 16 and 15.
The IPS-LCD device 1 is a conventional single-domain IPS-LCD device. This type of IPS-LCD device has the following inherent problem. Because the pixel and common electrodes 16 and 15 are all oriented in a single direction, the liquid crystal molecules are rotated in a single direction only. This means that an associated display screen exhibits color shift when the display screen is obliquely viewed while displaying white.
It is desired to provide an improved liquid crystal display device which overcomes the above problem.